The fluorene ring system and its numbering is demonstrated with the following formula:

Commonly known divinylfluorene compounds belong to the following (2,7-distyryl) core structure (I):

The unsubstituted compound of formula (I), wherein R and R′ each represent a hydrogen atom and the disubstituted compounds, wherein both R and/or both R′ represent a substituent selected from e.g. a hydroxy, alkoxy, dialkylamino, diarylamino or halogen group, are described in e.g. U.S. Pat. No. 3,980,713, US 2003/091859, GB 2 313 127 and U.S. Pat. No. 6,344,286.
For use as a luminescent material for organic and polymer-based electroluminescence elements, the distyryl fluorene compounds can also be polymerized or copolymerized as described e.g. in US 2003/091859.
Besides the aforementioned distyryl fluorene compounds (I) are also known the following di(vinyl hetaryl)fluorene compounds (F-1) and (F-2):
see e.g. Makromolekulare Chemie (1975), 176(3), 539-59, and
see e.g. JP 10 152 678 A2.
Apparently there is only known a very limited number of divinyl fluorene compounds from the prior art and such known compounds have drawbacks with respect to their properties when used as a) sensitizers for e.g. printing plate precursors, b) optical brighteners or c) monomers used for the preparation of electroluminescence elements.
When used as sensitizers for e.g. printing plate precursors, the sensitivity of the known compounds is still unsatisfactory and frequently there are observed so-called pinhole defects, that have an irregular crystal-like shape. Defects called pinholes are areas having lateral dimensions of about 50 to 500 μm on the processed printing plate, that don't take up ink and therefore result in exposed areas that don't print. This unfavorable effect is particularly noticeable, if the printing plate precursor is stored before exposure and processing thereof.
When used as optical brightener, there is a demand to have a broader range of substances to best fit the absorbance and emittance spectra as well as to increase the quantum efficiency. There is further a need to find optical brighteners that can easily be formulated and then incorporated in the material.
When used in polymeric form for electroluminescent elements, there still is a need for a broader range of compounds that allow the production of uniform films and that have an improved stability.
The synthesis of divinyl fluorene compounds is e.g. disclosed in U.S. Pat. No. 3,980,713. Said synthesis is carried out by a palladium catalyzed reaction of a vinyl benzene with a 2,7-dihalogenofluorene compound. This method is disadvantageous, as many vinyl aryl compounds like e.g. 3,4,5-trialkoxystyrene, 3,5-dialkoxy-4-hydroxystyrene or vinyl hetaryl compounds are not readily available. A similar method with the same restrictions is described in U.S. Pat. No. 6,344,286 and US 2003/091859.
From GB 2 313 127 is known a synthetic route to polymers comprising 2,7-distyrylfluorene monomers, wherein the polymers are formed by Wittig reaction of 2,7-bistriphenylphosphonium methylene-9,9-dialkylfluorene with dialdehydes. From the description is also known the synthesis of 2,7-dibromomethyl-9,9-dialkyl fluorenes by a) 9,9-dialkylation and b) 2,7-dibromomethylation of fluorene. The synthetic method is disadvantageous, as the product can not easily be purified.
From A. Patra et al., Chemistry of Materials (2002), 14(10), 4044-4048, is known a Wittig reaction on only one side of the fluorene unit using Diphenylaminobenzaldehyde.
According to J. M. Kauffman and G. Moyna, Journal of Organic Chemistry (2003), 68(3), 839-853, 2,7-bis-phosphonate esters of fluorene can be reacted with p-substituted aldehydes to yield 2,7-distyrylfluorenes. The disadvantage of this method is, that 5 reaction steps are necessary to obtain the 2,7-distyrylfluorenes from 9,9-dialkyl-2,7-dibromofluorene which itself must be prepared by alkylation of 2,7-dibromofluorene.
O. Mongin et al. describe in Tetrahedron Letters (2003), 44(44), 8121-8125, a synthetic method, wherein 9,9-dialkylfluorene is first converted to 2,7-dibromo-9,9-dialkylfluorene and then to 2,7-diformyl-9,9-dialkylfluorene. This is then reacted with [4-(dibutylamino)phenyl]methyltriphenylphosphonium bromide. The drawback is, that arylmethyltriphenylphosphonium salts are not readily available, relative to the analogous aldehydes.
From the foregoing discussion it becomes evident, that the known synthesis methods for divinylfluorene compounds are still unsatisfactory.